THE PROBABILITY OF SEA LEVEL RISE |
| The Earth's average surface temperature has risen
approximately 0.6°C (1°F) in the last century, and the nine warmest years have all
occurred since 1980. Many climatologists believe that increasing atmospheric
concentrations of carbon dioxide and other gases released by human activities are warming
the Earth by a mechanism commonly known as the "greenhouse effect."
Nevertheless, this warming effect appears to be partly offset by the cooling effect of
sulfate aerosols, which reflect sunlight back into space. Climate modeling studies generally estimate that global temperatures will rise a few degrees (C) in the next century. Such a warming is likely to raise sea level by expanding ocean water, and melting glaciers and portions of the Greenland Ice Sheet. Warmer polar ocean temperatures could also melt portions of the Ross and other Antarctic ice shelves, which might increase the rate at which Antarctic ice streams convey ice into the oceans. Warmer polar air temperatures, however, would probably increase annual snowfall, which would partly offset the rise in sea level caused by warmer temperatures. Along much of the United States coast, sea level is already rising 2.5-3.0 mm/yr (10 to 12 inches per century). By ratifying the United Nations Framework Convention on Climate Change, more than 120 countries have agreed to implement measures for adapting to rising sea level and other effects of changing climate. Because the design and location of coastal structures involve decisions that cannot be easily reversed, people responsible for these activities must either plan now or risk losing the opportunity for a meaningful response. Nevertheless, the value of planning for sea level rise depends upon the probability that the sea will rise by a given magnitude. The estimates of sea level rise are somewhat lower than those published by previous IPCC assessments, primarily because of lower temperature projections. This report estimates that global temperatures are most likely to rise 1°C by the year 2050 and 2°C by the year 2100, that there is a 10 percent chance that temperatures will rise more than 4°C in the next century, and a 90 percent chance that they will rise by at least the 0.6°C warming of the last century. By contrast, IPCC (1992) estimated that a warming of 2.8°C was most likely. Our temperature estimates are lower because (a) we assume lower concentrations of carbon dioxide; (b) we include the cooling effects of sulfates and stratospheric ozone depletion; and (c) our panel of experts included a scientist who doubts that greenhouse gases will substantially increase global temperatures. |
| Based on the aforementioned assumptions, results can be summarized! |